1. Field of Invention
The present invention relates to liquid crystal display (LCD). More particularly, the present invention relates to a pixel structure with multi-domain vertical alignment (MVA) design suitable uses in LCD.
2. Description of Related Art
Displaying device is very common in the daily life. Especially, a displaying device cannot be absent in a television set or a computer system, where the displaying device is used to display image to the user. In general, if the displaying device is designed by the cathode-ray tube (CRT) manner, it occupies a large space, causing inconvenient use. For example, a notebook cannot be equipped with a CRT display. In these considerations, a panel displaying device with matrix of pixels is successfully developed. The panel displaying device includes, for example, a liquid crystal display (LCD), or a thin film transistor (TFT) liquid crystal display (TFT-LCD).
The working principle of a twisted nematic (TN) LCD is schematically shown in FIG. 3. A liquid crystal layer 108 is confined between a glass plate 106. A polarizing layer 104 is arranged on the outer side of the glass plate 106 at the both sides, but the polarization direction is vertical to each other. For the left situation in FIG. 3, the incident light is polarized into one direction after the light passes the polarizing plate 104. The polarized incident light then enters the liquid crystal layer 108. When the liquid crystal layer 108 is not applied with a bias, the liquid crystal molecules are twisted by 90 degrees from one side to the other side. Since the polarizing plates 104 for the two sides have vertical polarization direction, the incident light can pass the lower polarizing plate 104.
If the liquid crystal layer 108 is applied with bias, such as the right situation in FIG. 3, the liquid crystal molecules are changed to a line structure. In this manner, the polarization direction of the incident light does not change. Since the lower polarizing plate 104 has the 90 degree rotated to the upper polarizing plate 104, the incident light can not pass the lower polarizing plate when the liquid crystal material is applied with bias.
Typically, the liquid crystal layer with respect to the substrate is divided into many pixels as a unit for displaying image. The shape of the pixel usually is a quadrate. In order to have better quality of vision angle for the LCD, the pixel is further divided into multiple regions, that is, a multi-domain vertical alignment (MVA) design.
FIGS. 1A and 1B are drawings, schematically illustrating a conventional pixel structure with the MVA design, where FIG. 1A is a top view and FIG. 1B is a cross-sectional view along the line I-I in FIG. 1A. The LCD includes a lot of pixels to display an image, here the drawing only shows one pixel structure for descriptions. In FIGS. 1A and 1B, the pixel structure of LCD includes an upper substrate 52, a lower substrate 56, and a liquid crystal layer 54 between the substrates. The liquid crystal molecule shape is elliptic. The pixel typically is a baguette.
In order to have multiple domains in one pixel, a surface of the upper substrate 52 adjacent to the liquid crystal layer 54 has several extruding lines 58 aligned in parallel. The lower substrate 56 has slits 60 in a discontinuation manner. The slits 60 are also arranged into a line parallel to the extruding lines 58 but between them.
In FIG. 1B, mechanism of the MVA design is further shown. When the liquid crystals are properly applied with the bias, the liquid crystals orients and become vertical to the surface for the substrate 52. However, due to the extruding line 58 and the slit 60, the oriented directions of the liquid crystals are not uniform, so that a multiple domains are obtained. The mechanism of MVA should be understood by the skilled artisans, no further description is made here.
Even though the MVA design principle has been proposed, technologies for how to effectively achieve the multiple domains with clear separation is still under developing. The extruding 58 associating with the slits 60 can divide the pixel into several domains but the domain boundaries are still not well defined.